While you can't actually make out a pocket knife in the footage, it's obvious George is finagling with the device ... before he tosses it on the ground.

Shellie recovers the iPad moments later.

After the incident, Shellie turned the iPad over to cops -- and they're confident they can recover any footage that was stored in the device, but acknowledge it was pretty badly damaged.

As we previously reported, Shellie initially told the 911 operator George was threatening the family with a gun ... but she later recanted her story and police say they've seen no evidence George ever had a gun.